Desiccant based air dehumidification offers the advantage of improving indoor air quality through the process of co-sorption of both moisture and the various gaseous pollutants common to incoming outside air OSA or mixed outdoor air and recirculated indoor return air RA. Additionally, desiccant dehumidification of air by solid desiccants captures and removes certain particulates from such air. This invention is particularly concerned with desiccant wheels and discriminate use of desiccants including molecular sieves, activated carbon, silica gel, polystyrene sulfonic acid lithium salt (PSSA-Li), alumina, zeolite, lithium chloride, etc. that will co-adsorb moisture and gaseous pollutants by adsorption.
Among gaseous pollutants known to be subject to co-adsorption are Volatile Organic Compounds VOCs which are detremental and harmful when concentrated, and among which are trichlorethane, toluene, benzene, formaldehyde, etc. Also, gaseous pollutants include radon, carbon dioxide and carbon monoxide. Particulate pollutants are respirable particles, for example those below 10 microns, and viable or living micro organisms that often propagate and grow in air conditioning ducts. The surface characteristics of solid desiccant used in dehumidifier wheels offer the properties necessary for water vapor and gaseous pollutant adsorption, and for volatile organic compounds VOCs as well.
Desiccant regeneration is effective within a wide range of temperatures from 130.degree. to 300.degree. F., it being an object of this invention to recover a large portion of this heat and thereby minimize heat loss to atmosphere in the exhaust of relief air RE.
Pollutant removal from both incoming outside air OSA and recirculated supply air SA is provided herein by both particulate filtration and by gas adsorption, the desiccant dehumidifier wheel as it is described herein is a gas adsorber that captures gasses and vapors, including Volatile Organic Compounds VOCs during the dehumidification phase, and discharges the same during the regeneration phase of dehumidifier operation. The particulate pollutants are removed by filter collection.
This invention deals with outside air OSA pollution as well as indoor air pollution generated by building materials, appliances, furnishings, and by human occupancy, all of which generates air pollution.
There is a wide variety of volatile chemicals that can be removed from the air being conditioned, for example, the presence of carbon dioxide is a known indication of building occupancy contamination, though it is not in itself dangerous, and it is known that building inhabitants emit gasses other than CO.sub.2 (i.e. methane) which have high reduction potentials, there being a broad range of chemicals which pollute the air, especially Volatile Organic Compounds VOCs, as follows:
______________________________________ Hydrogen Sulfide H.sub.2 S Vinyl Chloride C.sub.2 HC.sub.3 CL Methyl Ethyl Ketone C.sub.4 H.sub.8 O Hydrogen H.sub.2 Metheanol CH.sub.4 O Gasoline C.sub.x H.sub.x (x is variable) Formaldehyde CH.sub.2 O Trichloroethylene C.sub.2 HCL.sub.3 Acetone C.sub.3 H.sub.6 O Ethanol C.sub.2 H.sub.6 O Freon 22 CHCIF.sub.2 Ammonia NH.sub.3 ______________________________________
and others such as Freon 12, Propane, Methane, Methyl Chloride, Carbon Monoxide, Nitrogen Dioxide and Chlorine.